Spiral stairways are difficult to erect because the conditions of installation vary from one job site to another. This is because spiral stairways are often used in limited spaces, which require that the first and last steps meet predefined landings, and that all intermediate steps are equally spaced in both height and radial displacement from each other. This causes the radial spacing of the stair steps and the overall angle of inclination of the stairway to necessarily differ. Varying step locations about a center pole necessitates varying the positioning of accompanying pickets and railings.
It is precisely the above complexity in constructing a conventional spiral stairway that prompts most individuals to have them professionally built. The same complexity, however, exists for the manufacturer, because each installation must typically still be custom-made.
Therefore, what is needed is a spiral stairway having a railing assembly that may be easily and inexpensively manufactured; easily installed by both professionals and non-professionals; and easily adapted for a variety of installations. Such a spiral stairway and railing assembly would dramatically reduce or even eliminate the amount of unique tailoring that is currently required for conventional spiral stairways and railing assemblies.
U.S. Pat. No. 4,138,094 describes an adjustable railing assembly for straight, non-spiral stairways, where elongated inner retainers are secured in upper and lower rails. The inner retainers include a strip of material having equally spaced sockets therealong for receiving multiple baluster ends having cylindrical formations. Each retainer is T-shaped and is first loaded with balusters and is then slid into a rail. Alternatively, the retainer is rectangular and is positioned in a U-shaped rail, where a bolt secures the retainer in the rail. Either embodiment of this device has the disadvantage of being very difficult to use with spiral stairways, since either would require the manufacture of a long, curved retainer with sockets custom-made according to the particular spiral stairway specifications. The variations in angular orientation and spacing of the balusters in a straight stairway are not nearly as great as the potential angular orientation and picket spacing variations in a spiral stairway. This leads to precisely the custom attention the present invention seeks to avoid. The first embodiment additionally has the disadvantage of requiring the long curved T-shaped retainer to be slid longitudinally within a curved rail to load the baluster.
U.S. Pat. No. 4,928,930 describes an adjustable railing assembly where small individual retainers house cylindrical baluster ends, each retainer being slidably received in a slot formed in a rail. The device of this patent also requires custom routing of the slots and slot positions within a rail. This system would not be feasible for use in a spiral stairway kit because of the greater variety of positioning required for spiral stair installations.
It may be seen that what is needed is an adjustable spiral stairway kit having an adjustable railing assembly, where both the kit and the railing assembly are easy to manufacture, easy to adjust to fit a particular installation, and easy to install and maintain. The present invention provides such a device.